Many high value products can be produced from algal oil (e.g., microalgal oil, cyanobacteria oil), but obtaining the products requires numerous processing steps, such as extraction and transesterification, where efficiency and product mass can be lost at each step in the process. For example, biodiesel production from algal oil conventionally involves oil extraction followed by transesterification to produce fatty acid methyl esters (FAME). The majority of transesterification processes use a strong base to catalyze the reaction because it only requires moderate conditions and has a faster reaction time than an acid-catalyzed process, which tends to be slower due to the equilibrium. An acid catalyzed process is commonly used for biomass feedstocks with high free fatty acid content where soaps are not desired, because these high free fatty acid feedstocks may form soaps if a base catalyzed process is utilized in an attempt to form esters. Enzymatic transesterification is an emerging technology utilizing an enzyme catalyst to produce FAME from algal oil, but currently is not cost-effective due to issues with catalyst regeneration.
Direct transesterification (i.e., in-situ transesterification) of algal biomass is less time consuming and is more efficient than a conventional extraction transesterification process due to the inherent nature of a single-stage reaction, which comprises a reduction in process steps and material handling where the target product may be lost. Direct transesterification has been used (Johnson & Wen, 2009) to produce biodiesel from Schizochytrium limacinum using an acid catalyzed transesterification process with methanol, chloroform, hexane and/or petroleum ether solvents. In-situ transesterification and factors such as stirring, moisture content, and reaction temperature were also studied for production of biodiesel in Ehimen et. al (Ehimen, Sun, & Carrington, 2010). Biodiesel production methods were simplified by Wagner et. al (Haas & Wagner, 2011) and Mi et. al (Xu & Mi, 2010) using excess reagents and a co-solvent strategy respectively. Currently direct transesterification of algae technology focuses on production of FAME for biodiesel using high temperature and excess solvents in an inefficient manner.
Transesterification of triglycerides and fatty acids to produce esters has been performed using catalyst/conditions, such as: enzymes (Fjerbaek, Christensen, & Norddahl, 2009) (Modi, Reddy, Rao, & Prasad, 2007) (Mata, Sousa, Vieira, & Caetano, 2012); acid/base catalysts (Rodri & Tejedor, 2002) (Alamu, Waheed, & Jekayinfa, 2008); or heterogeneous catalysts (Zabeti, Wan Daud, & Aroua, 2009) (Liu, He, Wang, Zhu, & Piao, 2008). Previously, specific fatty acids or their esters have been purified from mixtures of fatty acids or their esters by molecular distillation into a form that is more useful for end products (Rossi, Pramparo, Gaich, Grosso, & Nepote, 2011) (Tenllado, Reglero, & Torres, 2011).
The focus on direct esterification method development in the biofuel art using methyl esters has not produced an efficient method translatable to other high value products derived from algal biomass. Therefore, there is a need in the art for an efficient method of esterification for ethyl esters of high value products from algal biomass.